1. Field of the Invention
The present invention relates to a developer cleaning method in a liquid electrophotographic printer, and more particularly, to a developer cleaning method for a liquid electrophotographic printer for removing powdered toner particles from the developer remaining on a photoreceptor medium and a development roller, after termination of a development mode, so that contamination of the photoreceptor medium and a transfer roller can be reduced.
2. Description of the Related Art
In general, a liquid electrophotographic printer such as a laser printer or copier develops an electrostatic latent image formed on a photoreceptor medium such as a photoreceptor web, using developer. The developed image is transferred to a sheet of paper via a transfer roller. The developer is formed by mixing toner powder having a predetermined color, and a liquid carrier.
Referring to FIG. 1, a conventional liquid electrophotographic printer includes a photoreceptor web 10 circulating by being supported by a plurality of guide rollers 11. In a development mode, while the photoreceptor web 10 circulates, a surface of the photoreceptor web 10 is charged to an electrical potential of about 600 V by a main corona 12. Subsequently, the charged surface of the photoreceptor web 10 is charged to an exposure electrical potential of about 150 V by a beam scanned by a laser scanning unit (LSU) 13 according to image signals so that an electrostatic latent image is formed. Reference numeral 28 denotes a topping corona for increasing the electrical potential of the photoreceptor web 10 lowered after passing a development unit 20 so that the electrical potential thereof can be maintained constantly.
Also, as shown in FIG. 2, developer is injected from an injection nozzle 23 toward the outer circumference of a development roller 22. The developer is transferred from the outer circumference of the development roller 22 to an area for the electrostatic latent image charged to an exposure electrical potential lower than that of the development roller 22 due to the difference in electrical potential, to develop the electrostatic latent image.
Extra developer on the surface of the photoreceptor web 10 is removed by a squeegee roller 24. The developed image is dried by a drying unit 15 and then transferred to a transfer roller 16 due to the difference in a surface energy. The transferred image is printed on a sheet of paper P passing between the transfer roller 16 and a fixation roller 17.
When the development mode is terminated, the supply of developer from the injection nozzle 23 is stopped. In a state in which a development electrical potential is continuously applied to the development roller 22, as shown in FIG. 3, the development roller 22 is lowered a predetermined distance and developer D dripping from the photoreceptor web 10 is removed. For this, the squeegee roller 24 is reversed in a state in which the pressing force of the squeegee roller 24 to the photoreceptor web 10 is reduced. Then, the developer D is removed from the photoreceptor web 10 by the squeegee roller 24 and cleaned by a squeegee blade 26 contacting the squeegee roller 24.
Reference numeral 25 denotes a cleaning blade installed at the injection nozzle 23 for cleaning developer adhering to the outer circumference of the development roller 22 and reference numeral 27 denotes a brush roller for cleaning the outer circumferential surface of the development roller 22 by rotating in contact with the development roller 22.
However, remaining developer B remains, as shown in FIG. 4, at a contact portion between the squeegee roller 24 and the squeegee blade 26 after the drip developer D removing mode is terminated. The remaining developer B contains toner particles of about 3-3.5 wt % which causes to contaminate the photoreceptor web 10 and the transfer roller (16 of FIG. 1) in the subsequent development mode.
Also, when the supply of developer is stopped as the development mode is terminated, developer already supplied remains due to a surface tension between the injection nozzle 23, the development roller 22 and the cleaning blade 25. As the remaining developer is hardened as the time passes, the image area is contaminated in the subsequent print mode.